Phytoplankton–zooplankton relationships based on phytoplankton functional groups in two tropical reservoirs

The aim of this study was to evaluate the phytoplankton–zooplankton interaction, using phytoplankton morphology-based functional groups, in two reservoirs that have different trophic state indices (TSIs). We hypothesised that the herbivorous relationships of zooplankton with the phytoplankton community would differ between reservoirs with different TSIs. In order to test this hypothesis, field collections to study the phytoplankton, zooplankton and abiotic variables were undertaken between July 2016 and April 2017 from the subsurface layer and in situ experiments were conducted using biomanipulation of the micro- and mesozooplankton. In situ experiments consisted of 18 microcosms in 5-L transparent plastic bottles (in triplicate). The mesotrophic reservoir showed predominance of chlorophytes (Group IV) and mesozooplankton during the study period. In the presence of zooplankton, all phytoplankton groups showed negative growth rates and higher ingestion values, mainly Group IV. In the supereutrophic reservoir, ingestion rates showed that micro- and mesozooplankton reduced the biomass of colonial (Group VII) and filamentous (Group III) cyanobacteria respectively. The findings of the present study reveal that Copepoda Calanoida, as well as small cladocerans, may be the most suitable zooplankton groups for biomass biomanipulation of different morphofunctional phytoplankton groups in mesotrophic reservoirs, and for the control of cyanobacteria in supereutrophic reservoirs.